As a known IGBT structure, for example, Japanese Patent Application Publication No. 2008-177297 discloses a semiconductor device including an upper drift region, separated from an n type emitter region by a p type body region, a p type floating semiconductor region, formed therebelow and being in an electrically floated state, an n type lower drift region, formed therebelow and being electrically continuous with the upper drift region, a trench, extending from a front surface of the emitter region so as to penetrate through the body region and the upper drift region and having its bottom surface projecting to the lower drift region, and a trench gate electrode, accommodated inside the trench in a state of being surrounded by an insulating layer covering its inner surface.